Photochemistry and Vibrational Spectra of Matrix-Isolated Methyl (2z)-2-Azido-3-Chloro-4-Oxo-4-Phenylbut-2-Enoate

SUSY LOPES, ANDREA GÓMEZ-ZAVAGLIA, RUI FAUSTO

Turín, Italia

Congreso; 41st IUPAC World Chemistry Congress. Chemistry Protecting Health, Natural Environment and Cultural Heritage.; 2007

IUPAC

Organic azides are a versatile class of compounds used as reagents in many fields. Due to their strong reactivity, azides play a crucial role in organic synthesis, in particular in heterocycle chemistry [1-2] and have important biological, pharmaceutical and industrial applications [3-5]. Thus, for example, azidonucleosides attract international interest in the treatment of AIDS [6-7]. They are also used on the preparation of semiconductor materials [8] and as high-energy density materials used in solid propellants and explosives [9-10]. In the present study, methyl (2Z)-2-azido-3-chloro-4-oxo-4-phenylbut-2-enoate (MACOPE; Figure 1) has been synthesized and its monomeric form studied by DFT calculations. A systematic search of the preferred conformations of MACOPE on the ground state potential energy surface and their vibrational spectra was performed with the Gaussian 03 program at the DFT(B3LYP)/6-311++G(d,p) level of theory. Figure 1 - Molecular structure of MACOPE The photochemical behavior of the studied novel haloazidoalkene was also investigated in low temperature matrices (argon, xenon) by infrared spectroscopy. The (Matrix Isolation)/ (Infrared Spectroscopy) technique was sellected as main experimental technique because it is an extremely powerful tool to undertake detailed structural and photochemical studies of molecules possessing several low energy isomeric forms. Indeed, in this technique, the compound under investigation is isolated in an inert cryogenic inert matrix at very low temperature and concentration. The technique takes then also advantage of the relative rigidity of the matrix, which inhibits diffusion and minimizes the chance of interaction between the particles. As it is relatively easy to start photochemical reactions in a matrix by irradiating the sample at specific wavelengths, this technique is also very powerful when used for both the identification of possible photoproducts and characterization of the associated mechanisms [11]. In the present study, matrices were prepared by co-deposition of MACOPE vapors together with a large excess of the matrix gas (argon; xenon) onto the cold optical CsI substrate of the cryostat. Then, in situ broadband irradiation was undertaken using a standard 150 W xenon lamp as UV-light (l > 235 nm) source through the external KBr window of the cryostat as a cut-off filter. The interpretation of the IR spectra of the compound isolated in the different matrices investigated and the identification of the resulting photoproducts were supported by theoretical calculations undertaken at the DFT(B3LYP)/6-311++G(d,p) level of approximation. [1] Patai S., The Chemistry of the Azide Group, Interscience Publishers: New York (1971). [2] Scriven E., Turnball K., Chem. Rev. 88 (1988) 298. [3] Baran P. S., Zografos A. L., and O’Malley D. P., J. Am. Chem. Soc. 126 (2004) 3726. [4] Greenberg W. A., Priestley E. S., Sears P. S., Alper P. B., Rosenbohm C., Hendrix M., Hung Sh.-Ch. and Wong Chi-W., J. Am. Chem. Soc. 121 (1999) 6527. [5] Bräse S., Gil C., Knepper K. and Zimmermann V.; Angew. Chem. Int. Ed. 44 (2005) 5188-5240. [6] Piantadosi C., Marasco C. J., Morris-Natschke S. L., Mayer K. L., Gumus F., Kucera L.S., Iyer N., Wallen C. A., Piantadosi C. and Modest E. J., J. Med. Chem. 34 (1991) 1408. [7] Pathak P., Chem. Rev. 102 (2002) 1623. [8] Meijer E. W., Nijhuis S. and van Vroonhoven F. C. B. M., J. Am. Chem. Soc. 110 (1998) 7209. [9] Kubota N., J. Propul. Power 11 (1995) 67. [10] Badri M. and Mooney H. M., Geophysics 52 (1987) 772. [11] Fausto R., Low Temperature Molecular Spectroscopy, NATO-ASI Series, Vol. 483, Ed. Fausto R., Kluwer, Dordrecht, NL, (1995) page 125. Acknowledgements: This work was funded by FCT (Projects POCTI/QUI/59019/2004 and POCTI/QUI/58937/2004), and the Instituto de Investigação Interdisciplinar of the University of Coimbra (Project III/BIO/40/2005). S.L. acknowledges FCT the Ph.D. grant (SFRH/BD/29698/2006).